This invention relates to a robotic manipulator system that obtains position information of a work component and/or a controllable tool using radio positioning technology to assist in automatic manufacturing processes. Robotic manipulators have been used in automatic manufacturing environments for many years, and their use is growing at a rapid pace. Robotic manipulators can, in many instances, out perform human labor performing similar operations. Radio positioning techniques are also known and are used extensively in the navigation of airplanes, marine vessels, automobiles, construction equipment, and other applications. The most popular form of existing radio navigation is the well-established NAVSTAR Global Positioning System (GPS).
Robotic manipulators serve many different manufacturing functions but are different than single purpose machines performing what is known as “hard automation.” Hard automation machines are designed and configured to repetitively perform a single tasks, and normally perform that task with great efficiency and speed. The primary distinction between robotic manipulator systems and hard automation machines is the programmable flexibility of the robots. The International Standards Organization (ISO) defines industrial robots in standard ISO/TR/8373-2.3:                A robot is an automatically controlled, reprogrammable, multipurpose, manipulative machine with several reprogrammable axes, which may be either fixed in place or mobile for use in industrial automation applications.Most single purpose hard automation machines do not meet the requirements of reprogrammable or multipurpose. Although multipurpose robotic manipulators typically have a higher initial cost and slower speeds than hard automation devices they replace, they usually reduce overall manufacturing costs by reducing the total number of machines required to handle all of the processes involved in a single manufacturing environment.        
Initially robotic manipulators were replacements for humans in the manufacturing process. As the role of robotic manipulators increased to broader areas of manufacturing, the need for a more structured approach to their functioning became apparent. Robotics is combined with modem computer technology as part of Computer Integrated Manufacturing (CIM) systems. CIM concepts guide manufacturers through the process of planning and identifying automation hardware and software requirements for a particular product. Additional background material on robotics fundamentals can be found in the following publications, each of which is incorporated herein by reference: Rehg, James A., Introduction to Robotics in CIM, Prentice Hall, New Jersey (2000), ISBN 0139012087; Ardayfio, David D., Fundamentals of Robotics, Marcel Dekker, Inc., New York (1987), ISBN 082477440X.
Typical robotic systems have a mechanical arm attached to a fixed base or attached to a railing or overhead gantry system providing a horizontal and/or vertical axis of movement. The robotic arm provides the motion required to attain proper positioning of an end effector so the robotic system can perform the desired task on a work piece. The end effector is the part of the mechanical arm that holds a tool, performing such tasks as cutting, welding, fastening, tapping, drilling, etc. or grasps a part to be placed or removed on an assembly. There are many types of end effectors that can be attached to the end of any given robotic arm to provide flexibility in performing multiple manufacturing tasks.
Robotic arms can be categorized into four basic geometries: Cartesian, cylindrical, spherical, and articulated. The different geometries have advantages and disadvantages that must be considered when specifying a robotic manipulator system for a particular manufacturing environment. Each of the four geometries has a range of useful arm movements that creates what is referred to as the “work envelope.” Articulated robots, also known as anthropomorphic robots, allow the most complex type of movements but has the tradeoff of requiring the most sophisticated controlling hardware and software.
Another factor determining the flexibility of a robotic system is the number of axes, or degrees of freedom (DOF), that the robotic system exhibits. Each driven link in a robotic arm provides for one degree of freedom. Most robotic arms have at least three degrees of freedom, and having six or seven is not uncommon. Having a robotic system with more degrees of freedom allows for more complex manufacturing tasks to be undertaken. Many robotics systems have been devised or existing systems improved upon as seen in U.S. Pat. Nos. 6,105,455; 6,074,164; 5,893,296; 5,871,248; 5,845,540; 5,811,951; 5,694,813; 5,692,412, each of which is incorporated herein by reference.
GPS is a well-established radio navigation technique based on the use of a constellation of twenty-four satellites in carefully placed geo-synchronous orbits. Ground control stations monitor and correct the performance of the satellite broadcasts to maintain a high level of accuracy. Receivers on the earth lock onto ranging signals from multiple satellites and calculate receiver position (latitude, longitude, and elevation) using a mathematical technique known as trilateration or resection. Initially the GPS system provided two modes of operation, the standard positioning system (SPS) signal and the precise positioning system (PPS) signal used by the military. The SPS is lower precision version of the PPS meant for use by the general public, while the improved PPS was restricted for use by the military. Selective Availability (SA) was employed to additionally reduce the precision of the SPS. As engineering accomplishments reduced the error due to SA, it became obsolete and was removed from operation. All sectors of GPS users now have access to the more accurate SPS.
Even with the more accurate SPS, position errors are inherent in the positioning determining process due to atmospheric distortion, multi-path, and other factors. The GPS satellites are in orbits of about 11,000 miles, degrading the positioning signal as it passes through the ionosphere and troposphere. The positioning signal can also bounce off mountains, buildings, or other interfering objects creating one or more delayed signals giving rise to a condition known as “multi-path.” Other positioning errors are experienced by GPS receivers due to clock and ephemeris (orbit) error. Errors also arise due to receiver “noise” in the electrical/electronic context. The following table is a summary of GPS error sources [“Trimble—How GPS Works,” available on the Trimble Co. internet website as of Jul. 2, 2001]:
Error SourceTypical Error in Meters (per satellite)Satellite Clocks1.5Orbit Errors2.5Ionosphere5.0Troposphere0.5Receiver Noise0.3Multipath0.6
The need to minimize the effects of the GPS positioning errors led to the development of the Differential Global Positioning System (DGPS). If a position on earth is known very precisely, the position error for that position, for any given time of day, can be determined. DGPS ground stations with precise known positions broadcast error information for a particular geographic region. DGPS adds to system cost and is not always necessary, but it is usually found in high population areas. Many concepts and systems for control of vehicles or other processes using GPS and DGPS positioning exist. For instance, see U.S. Pat. Nos. 6,161,072; 6,052,647; 6,035,254; 6,032,084; 6,024,655; 5,995,882; 5,983,161; and 5,438,771, each of which is incorporated herein by reference.
Locational reference systems are important to radio positioning as they define an area in which the positioning effort is to be performed. Earth-based locational reference systems are used to define the irregularities of the earth for more precise positioning. There are many different types of earth-based locational reference systems, the simplest of which is a sphere. More complex reference systems are based on an ellipsoidal earth and complex gravity models. Reference ellipsoidal models enhance distance and direction measurements over long distances. Reference ellipsoids are based upon the earths' irregular shape due to a slight flattening at the earth's poles.
More precise positioning requires more details about the irregularities of the earths' surface. The science of geodesy involves modeling of the earth using more complex techniques such as gravity models and geoids. Geodetic datum reference systems use these techniques to create more accurate models of the earth's surface. There are many different datums available with varying accuracy. The World Geodetic System 1984 (WGS 84) geodetic datum is globally accepted as the most accurate. GPS receivers typically have multiple geodetic datums on board for use in varied applications.
Another highly accurate implementation of radio positioning is relative GPS. Relative GPS is similar to DGPS in that it is assumed that two receivers in close proximity exhibit the same inaccuracies due to the signal path and processing performance limitations. The relative positions between two closely placed receivers can then be determined very accurately. The main difference between DGPS and relative GPS is the mobility of relative GPS. DGPS stations are at fixed locations. Relative GPS systems can be taken to work sites anywhere in the world and even used in applications where both GPS receivers are in motion. Systems are available that implement this concept of relative GPS. They are primarily used in surveying.
GPS receivers typically perform the calculations necessary to resolve their immediate position using raw position information from multiple satellites in line-of-sight locations. This implies having the necessary processing hardware and memory for storing datum and other information. Translated GPS is a concept where raw position signals from the receiver are translated to a different frequency and transmitted to a host site that performs the necessary calculations to determine the current position. This considerably reduces the hardware complexity and size of the receiver. Translated GPS is very useful in an environment where many small and inexpensive receivers are required.
Computer vision is used extensively in automatic manufacturing for object inspection, location determination, dimensional measurements and control of robotic manipulators. Computer vision systems used to determine object location typically employ pattern recognition. Such systems convert image signals generated using some form of imaging device to digital signals that can be processed with a computer. The location of a particular pattern is sought and when a “match” is found a programmed response can be implemented by the vision system. The controller for the particular manufacturing operation takes the appropriate action based on the response from the vision system. Representative art involving computer vision techniques include, but are not limited to, the following: U.S. Pat. Nos. 6,175,652; 6,173,070; 6,115,480; 5,949,901; 3,081,379; 3,854,889; 4,338,626; 4,118,730; 4,979,029; 5,119,190; 4,984,073; 5,067,012; 4,511,918; and 5,023,714. Additional background information can be found in: Aleksander, I., Artificial Vision for Robots, Chapman and Hall, New York (1983), ISBN 412004518. Each of the above patents and publications is incorporated herein by reference.